Update dependencies to latest versions

Left ASM at current version due to breaking API changes in ASM 5.0.1
Upgrade to Gradle 1.11
Use repo.spring.io rather than Maven Central

Resolve dependencies from repo.spring.io rather than Maven Central
Update Sonar configuration to be compatible with Gradle 1.11
Use repo.spring.io rather than Maven Central for sub-projects as well
Update URLs: springsource.org -> spring.io

Update URLs in the build files and the README to use the new
spring.io domain. The URLs in the generated migration reports have
not been updated.